1. Field of the Invention
The present invention relates to improved methods and apparatus for the contact planarization of surfaces such as those developed during the manufacture of advanced integrated circuits and other devices.
2. Description of the Prior Art
Advanced integrated circuit (IC) designs are highly dependent on complex device-layering techniques to produce semiconductor devices that are more powerful, have lower profiles, and require less energy to operate. To make these qualities possible, more circuits with much finer structures must be integrated into a microchip by constructing multiple layers of interconnects and dielectrics on a semiconductor substrate in an appropriate sequence. Currently, photolithography is the predominant technique used to pattern these ultra-fine structures. This technique requires materials to be deposited and removed from the surface to construct such ultra-fine structures.
Photolithography involves depositing a photosensitive material, known as a photoresist, onto a semiconductor substrate surface. An optical transparent object, known as the photomask or reticle, with pre-defined images of the structures to be built on the semiconductor surface is placed above the photoresist-coated substrate. An appropriate wavelength of light is then illuminated through the optical object. The light either decomposes or cures the exposed area of the photoresist, depending on the nature of the photoresist and the process. The semiconductor surface is then developed to produce the patterned image on the substrate surface, and the procedure is then repeated for additional layers.
Materials can be applied in a uniform thickness if the surface to be coated is entirely planar. However, if the surface is not planar, materials may not coat with a uniform thickness. For example, a coating deposited on top of a topographic surface tends to contour to the topography of the underlying surface, thus producing a non-planar surface. As more layers are built on the substrate, the severity of the surface topography increases. Unfortunately, non-planar surfaces reduce the final yield and performance of IC devices. Moreover, at some point of applying successive layers of structure to a non-uniform surface of an IC, the non-planar surface becomes unsuitable for constructing the next structural layer. Therefore, the topographic surface of the IC must be planarized, or flattened, prior to the construction of the next layer. To planiarize the topographic surface, techniques such as plasma etch-back, chemical mechanical polishing (CMP), and contact planarization can be used. The present invention relates to contact planarization techniques.
With prior art contact planarization techniques, the topographic surface is first deposited with a flowable planarization material. The surface is then pressed against a flat surface (optical flat) to cause the material to flow around the topographic structures. The material is then hardened by either photo-irradiation or heat to replicate the planarity of the flat surface onto the planarized material surface. The planarized material surface is then released from the flat surface. To facilitate the separation, the flat surface can be treated with a low friction material such as a fluoropolymer a fluorinated compound to lower its surface energy. Alternatively, a low surface energy material such as Teflon® materials, fluorocarbon polymers, or the like with comparable surface planarity, such as a disk or film, can be placed between the planarization material and flat surface.
Prior art devices suffer from several limitations. For example, the optical flat (and often other pieces of the apparatus) is interposed between the UV radiation or heat source and the substrate, and thus create a substantial thermal or UV absorbing mass which must be overcome to cure the underlying substrate. This substantially increases the cure time of the coating applied to the substrate, and thus reduces the throughput of the apparatus.
Another disadvantage of prior art contact planarization devices is that much of the planarization is achieved by sandwiching the substrate and its planarizable coating between a rigid substrate support assembly and a rigid optical flat assembly or other backing. Sandwiching the substrate between rigid structures to effect much of the planarization makes it difficult to precisely control the pressure applied to the substrate and its coating and the targeting of the pressure. Many prior art contact planarization devices also do not sufficiently evacuate air from the area around the substrate during planarization, causing unwanted air bubbles to be entrapped in the coating.
Accordingly, there is a need for an improved contact planarization apparatus and method that overcomes the limitations of the prior art.